Conventional piston engines and compressors use a crankshaft with an attached piston rod linkage, thereby causing limitations in the areas of efficiency, balance, noise, power shaft rpm reduction, weight and cost. These limitations are caused by six primary disadvantages: (1) Conventional crankshaft mechanisms oscillate the piston rods causing rod vibrations and piston side thrust resulting in piston friction. (2) Conventional crankshaft mechanisms have constraints for increasing piston dwell at the top of the stroke to improve engine efficiency. (3) Because of piston connecting rod angularity, conventional crankshaft mechanisms have non-harmonic piston motion which causes secondary inertia force vibrations for most arrangements. (4) For the operation of diesel engines, conventional crankshaft mechanisms cause piston knocking against the cylinder walls because of piston rod oscillations in combination with high combustion pressures. (5) Crankshafts require heavy counterweights for balance and transmissions for power shaft rpm reduction. (6) Conventional crankshafts require 4-stroke instead of 2-stroke operation for optimum efficiencies which result in increased weight and cost.
Diametrically-opposed piston, yoke crankshaft (scotch yoke) engines have been acknowledged for over 100 years. The scotch yoke engine has been given much consideration by a few manufacturers for replacing some conventional crankshaft engines. Today, several companies are continuing to develop and promote the yoke crankshaft engine in an attempt to establish acceptance by the public.
In U.S. Pat. Nos. 399,593; 2,122,676; 2,513,514; 4,013,048 and 5,331,926, there are disclosed yoke crankshaft engines. The crankpin carries a slider block or crankpin roller that rolls within the yoke-follower (yoke). The yoke-follower is connected to the ends of the piston rods; the pistons and rods reciprocate along a centerline perpendicular to and intersecting the crankshaft axis. Therefore, these engines eliminate piston rod angularity and provide harmonic piston motion that results in the benefits of longer piston dwell and less vibration.
With the opposed-piston yoke crankshaft engine, lateral movement of the crankpin with its attached roller causes piston side thrust against the cylinder walls and piston friction; but, less friction than conventional crankshaft engines for the same rod length. Because of the increased piston dwell at the top of the stroke and reduced piston friction, the yoke crankshaft engine efficiencies are substantially improved when compared to today's short to medium length piston rod conventional engines. However, a drawback for the present day yoke crankshaft is that for diesel engines the piston rods need to be extra heavy for supporting forces related to the lateral movement of the crankpin roller bearing.
The yoke crankshaft engine has a third advantage in that under-piston scavenging pumps can be provided for 2-stroke opposed-piston engine operation. Since the piston rods reciprocate along the axis of the cylinders, rod seals can be easily installed to seal off the crankcase allowing a low cost and compact means of self-aspirating 2-stroke engines. When operating as a 2-stroke two-cylinder engine with 180° alternating power strokes and using auxiliary balancing weights for low vibration, the yoke crankshaft engine becomes a formidable rival to the much more complex and expensive 4-stroke four-cylinder, horizontally-opposed or in-line conventional engine. Because of feasibility limitations, a drawback for present day yoke crankshaft engines is that they are limited to horizontal-opposed cylinder arrangements.
In attempting to overcome the kinematic disadvantages of the crankshaft mechanism, cam engines have been developed. Primary drawbacks for cam engines are structural complexity and increased expense which are caused by the difficulty in providing a simple means for maintaining cam followers in contact with the cam track. Cam engines generally have less piston friction and improved balance compared to crankshaft engines.
In U.S. Pat. Nos. 1,817,375; 2,124,604 and 4,697,552, there are disclosed single-plate three-lobe cam engines. These engines include slides or rollers for supporting the sides of links (linking-rods) that couple together diametrically-opposed pistons. Each link also connects two opposed roller cam followers that make contact on opposite sides of a three-lobe cam. The connecting pistons, followers and links reciprocate along a centerline perpendicular to and intersecting the cam axis, thereby promoting harmonic piston motion. The conventional art of guiding and supporting the links is a simple and low-cost linkage arrangement for maintaining the roller followers in contact with the cam, and these linkages serve many light duty machine applications such as typesetting, automatic packing, shoe making, etc. However, for heavy duty applications like engines and compressors, link side thrust and link friction become a problem. The above patents describe linking-rod engines which use heavy duty links to support the side thrust that is delivered from the attached roller followers. To provide link support and alignment, the links require precision bearing surfaces that maintain contact with precision aligned rollers or link guides; the link guides require high oil pressures to reduce friction and wear.
In U.S. Pat. Nos. 4,011,842 and 4,274,367, there are disclosed crankshaft beam engines that use a pair of attached longitudinal extending arms for providing a rocker beam (rocker lever). These engines have one beam which is connected to either one or two single-throw crankshafts for a single row engine. Disadvantages for these engines are cost, balance and limited to low piston speed applications. They require multiple unit-rows for good balance, and for single row applications require very large counter weights and still have poor balance. Because of virtually eliminating piston friction, these beam engines have been commercially successful for some low piston speed applications.
U.S. Pat. No. 2,417,648 discloses opposed pairs of beams for a four-lobe cam engine that was improved and built later as a two-lobe cam engine for marine and stationary applications by Svanemolle Wharf Co. of Copenhagen, Denmark. (Heldt in Auto. Ind., Jun. 15, 1955, “Two-stroke Diesel has no Crankshaft”) This engine met with limited success for some low rpm commercial uses. The two-lobe cam allows the elimination of transmissions for marine and some stationary applications. For one row, this double-opposed piston engine has the added advantage of 2-stroke operation using two opposed pistons in one cylinder with the cylinder positioned between the beams. For a one-row diesel, this engine has the disadvantages of requiring three cams with four roller cam followers, two auxiliary follower arms and heavy opposed beams. Also, this engine operates at very low piston speeds which further increase engine weight per bhp. Because of these disadvantages, the weight and cost of this 2-stroke beam engine are substantially increased when compared to conventional crankshaft engines.
Sulzer in Switzerland has been successful producing a somewhat similar type of opposed beam diesel engine which uses a two-throw crankshaft (instead of cams) with double-opposed pistons. For each row, the crankshaft throws are connected to a pair of offset crankshaft connecting rods which are connected to the offset ends of complex and heavy opposed pair of beams. Each piston requires a separate crankshaft throw, two connecting rods, a heavy beam and large housing, thereby increasing weight and cost that result in limited applications.
Prior art piston machines have many disadvantages that have been only slightly improved over the past decades. Engine efficiency, weight and cost, although somewhat improved, have not had substantial progress in these areas. Attempts have been made to replace the conventional crankshaft mechanism with various yoke crankshaft, cam and beam machine designs, but with limited success. Complexity, cost and marginal operational improvements have prevented these “improved” machines from coming to the forefront in today's marketplace. The present invention overcomes most of the disadvantages discussed in this “Background of the Invention” for the prior art crankshaft, cam and beam machines. Additionally, conventional engines use superchargers that are expensive, heavy and consume lots of space. The invention provides the novel use of under-piston pumps that overcome the disadvantages of the weight and expense characteristic of conventional superchargers while providing the same benefits of increased power, improved air-fuel mixing, fuel economy and lower emissions.